Solid-state imaging device, manufacturing method of solid-state imaging device and electronic apparatus

ABSTRACT

A solid-state imaging device includes a pixel having a photoelectric conversion element which generates a charge in response to incident light, a first transfer gate which transfers the charge from the photoelectric conversion element to a charge holding section, and a second transfer gate which transfers the charge from the charge holding section to a floating diffusion. The first transfer gate includes a trench gate structure having at least two trench gate sections embedded in a depth direction of a semiconductor substrate, and the charge holding section includes a semiconductor region positioned between adjacent trench gate sections.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of application Ser. No.16/028,818, filed Jul. 6, 2018, which is a Continuation of applicationSer. No. 15/470,535, filed Mar. 27, 2017, now U.S. Pat. No. 10,020,339,issued Jul. 10, 2018, which is a Continuation of application Ser. No.14/831,328, filed Aug. 20, 2015, now U.S. Pat. No. 9,608,036, issuedMar. 28, 2017, which is a Continuation of application Ser. No.14/331,742, filed Jul. 15, 2014, now U.S. Pat. No. 9,129,881, issuedSep. 8, 2015, which claims the benefit of Japanese Priority PatentApplication JP 2013-185945 filed Sep. 9, 2013, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND

The present technology relates to a solid-state imaging device, amanufacturing method of the solid-state imaging device and an electronicapparatus, and specifically, relates to a solid-state imaging devicethat can increase an amount of a saturated charges in a solid-stateimaging device capable of realizing a global shutter, a manufacturingmethod of the solid-state imaging device and an electronic apparatus.

In recent years, a CMOS solid-state imaging device (CMOS imaging sensor)is mounted on many electronic apparatuses such as a digital camera, avideo camera, a surveillance camera, a copying machine and a facsimile.

In the CMOS solid-state imaging device, in order to read chargesaccumulated in a photodiode for each row, a gap occurs at a time foraccumulating optical charges and distortion occurs in an object that isphotographed when the object moves.

In order to prevent the distortion in the object, an all-pixelsimultaneous electronic shutter in which exposure periods of each ofpixels are the same as each other is being developed. The all-pixelsimultaneous electronic shutter performs an operation in which theexposure is simultaneously started in all effective pixels in imagingand the exposure is simultaneously completed, and is also referred to asa global shutter (global exposure).

As a method for realizing the global shutter, for example, there is amethod in which in each pixel, a charge holding region is providedbetween the photodiode as a charge accumulation region and a floatingdiffusion region (FD: Floating Diffusion), and the charges accumulatedin the photodiode are simultaneously and temporarily transferred to thecharge holding region for all pixels, and the charges accumulated in thecharge holding region are read by performing sequential scanning foreach row.

For the charge holding region, a structure is used which has a PNjunction in which first conductivity type and second conductivity typesemiconductor regions are laminated in a semiconductor substrate, and aplanar type gate electrode that controls charge transfer through aninsulating film on an upper section of the PN junction (for example,Japanese Unexamined Patent Application Publication No. 2009-268083).

In the CMOS solid-state imaging device realizing the global shutter, itis necessary to hold a maximum amount (amount of saturated charges) of acharge signal that is accumulated in the photodiode in the chargeholding region.

SUMMARY

However, in order to increase a holding capacity of the charge holdingregion, when increasing an area of the charge holding region, an area ofthe photodiode is reduced, on the contrary. Thus, the area of thephotodiode for unit pixel size is reduced and light receptionsensitivity thereof or the amount of the saturated charges of thephotodiode is lowered compared to that of a non-global shutter type CMOSsolid-state imaging device.

In the present technology, it is desirable to increase an amount ofsaturated charges in a solid-state imaging device capable of realizing aglobal shutter.

According to an embodiment of the present technology, there is provideda solid-state imaging device comprising: a pixel including aphotoelectric conversion element configured to generate a charge inresponse to incident light, a first transfer gate configured to transferthe charge from the photoelectric conversion element to a charge holdingsection, and a second transfer gate configured to transfer the chargefrom the charge holding section to a floating diffusion, wherein thefirst transfer gate includes a trench gate structure having at least twotrench gate sections embedded in a depth direction of a semiconductorsubstrate, and the charge holding section includes a semiconductorregion positioned between adjacent ones of the plurality of trench gatesections.

According to another embodiment of the present technology, there isprovided a manufacturing method of a solid-state imaging device,comprising: providing a semiconductor substrate; forming a pixel on thesemiconductor substrate, the pixel including a photoelectric conversionelement configured to generate a charge in response to incident light, afirst transfer gate configured to transfer the charge from thephotoelectric conversion element to a charge holding section, and asecond transfer gate configured to transfer the charge from the chargeholding section to a floating diffusion, wherein the first transfer gateincludes a trench gate structure having at least two trench gatesections embedded in a depth direction of a semiconductor substrate, andthe charge holding section includes a semiconductor region positionedbetween adjacent ones of the plurality of trench gate sections.

According to still another embodiment of the present technology, thereis provided an electronic apparatus comprising: an optical section; asolid-state imaging device; and a digital signal processor circuit,wherein the solid-state imaging device includes: a pixel including aphotoelectric conversion element configured to generate a charge inresponse to incident light, a first transfer gate configured to transferthe charge from the photoelectric conversion element to a charge holdingsection, and a second transfer gate configured to transfer the chargefrom the charge holding section to a floating diffusion, wherein thefirst transfer gate includes a trench gate structure having at least twotrench gate sections embedded in a depth direction of a semiconductorsubstrate, and the charge holding section includes a semiconductorregion positioned between adjacent ones of the plurality of trench gatesections.

In the above embodiments of the present technology, the gate electrodeof the first transfer transistor is configured to have two or moretrench gate sections embedded from the interface of the semiconductorsubstrate to the predetermined depth, and the charge accumulationsection is formed vertically long between the two trench gate sectionsof the first transfer transistor embedded in the semiconductorsubstrate.

The solid-state imaging device and the electronic apparatus may be anindependent device or may be a module to be incorporated into otherdevices.

According to the above embodiments of the present technology, it ispossible to increase the amount of the saturated charges in thesolid-state imaging device capable of realizing the global shutter.

Moreover, the effects described here are not necessarily limited and anyof effects may be effective in the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a schematic configuration of a solid-stateimaging device to which the present technology is applied;

FIG. 2 is a view illustrating an equivalent circuit of a pixel;

FIG. 3 is a plan view illustrating a schematic configuration of thepixel in a first embodiment;

FIGS. 4A and 4B are cross-sectional views illustrating a schematicconfiguration of the pixel in the first embodiment;

FIGS. 5A to 5D are views describing a forming method of a memorysection;

FIG. 6 is a plan view illustrating a pixel structure of a planar typefirst transfer transistor;

FIGS. 7A and 7B are cross-sectional views illustrating the pixelstructure of the planar type first transfer transistor;

FIGS. 8A and 8B are views illustrating an impurity concentrationprofile;

FIGS. 9A to 9C are views describing a modification example of a formingmethod of a memory section;

FIG. 10 is a plan view illustrating a schematic configuration of a pixelin a second embodiment;

FIG. 11 is a cross-sectional view illustrating a schematic configurationof the pixel in the second embodiment;

FIG. 12 is a plan view illustrating a schematic configuration of a pixelin a third embodiment;

FIG. 13 is a cross-sectional view illustrating a schematic configurationof the pixel in the third embodiment;

FIG. 14 is a plan view illustrating a schematic configuration of a pixelin a fourth embodiment;

FIGS. 15A and 15B are cross-sectional views illustrating a schematicconfiguration of the pixel in the fourth embodiment;

FIG. 16 is a plan view illustrating a schematic configuration of a pixelin a fifth embodiment;

FIGS. 17A and 17B are cross-sectional views illustrating a schematicconfiguration of the pixel in the fifth embodiment; and

FIG. 18 is a block diagram illustrating a configuration example of animaging apparatus as an electronic apparatus to which the presenttechnology is applied.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present technology is described.Moreover, the description is made in the following order.

1. Schematic Configuration Example of Solid-State Imaging Device

2. Circuit Configuration Example of Pixel

3. First Embodiment (Configuration Example Having Two Trench GateSections) of Pixel

4. Second Embodiment (Configuration Example Having Three Trench GateSections) of Pixel

5. Third Embodiment (Configuration Example Having Light-ShieldingMaterial Inside Trench Gate Section) of Pixel

6. Fourth Embodiment (Configuration Example of Back Surface IrradiationType) of Pixel

7. Fifth Embodiment (Configuration Example Having PhotoelectricConversion Film of Back Surface Irradiation Type) of Pixel

8. Application Example to Electronic Apparatus

1. Schematic Configuration Example of Solid-State Imaging Device

FIG. 1 illustrates a schematic configuration of a solid-state imagingdevice to which the present technology is applied.

A solid-state imaging device 1 in FIG. 1 is configured to have a pixelarray section 3 in which each pixel 2 is arranged in a two-dimensionalarray and peripheral circuit sections in the periphery thereof in asemiconductor substrate 12 using, for example, silicon (Si) as asemiconductor. The peripheral circuit sections include a verticaldriving circuit 4, a column signal processing circuit 5, a horizontaldriving circuit 6, an output circuit 7, a control circuit 8 and thelike.

The pixel 2 is configured to have a photodiode as a photoelectricconversion element and a plurality of pixel transistors. A configurationexample of the pixel 2 is described below with reference to FIG. 2.

Further, the pixel 2 can also be a shared pixel structure. The sharedpixel structure is configured of a plurality of photodiodes, a pluralityof transfer transistors, one floating diffusion (floating diffusionregion) that is shared, and each of other pixel transistors that areshared. That is, in the shared pixel, the photodiode and the transfertransistor configuring a plurality of unit pixels are configured toshare another pixel transistor.

The control circuit 8 receives data for instructing an input clock, anoperation mode and the like, and outputs data such as internalinformation of the solid-state imaging device 1 and the like. That is,the control circuit 8 generates a clock signal or a control signal as areference for the operation of the vertical driving circuit 4, thecolumn signal processing circuit 5, the horizontal driving circuit 6 andthe like, based on a vertical synchronization signal, a horizontalsynchronization signal and a master clock. Then, the control circuit 8outputs the clock signal or the control signal that is generated to thevertical driving circuit 4, the column signal processing circuit 5, thehorizontal driving circuit 6 and the like.

For example, the vertical driving circuit 4 is configured of a shiftregister and selects a pixel driving wiring 10, and supplies a pulse fordriving the pixel 2 to the pixel driving wiring 10 that is selected, anddrives the pixels 2 on a row-by-row basis. That is, the vertical drivingcircuit 4 selectively scans each pixel 2 of the pixel array section 3sequentially in a vertical direction on a row-by-row basis and suppliesthe pixel signal to the column signal processing circuit 5 through avertical signal line 9, based on signal charges generated depending onan amount of received light in the photoelectric conversion section ofeach pixel 2.

The column signal processing circuit 5 is disposed for each column ofthe pixels 2 and performs a signal process such as noise removal foreach pixel column with respect to the signal output from the pixels 2 ofone row. For example, the column signal processing circuit 5 performsthe signal process such as a Correlated Double Sampling (CDS) forremoving fixed pattern noise unique to the pixel, and AD conversion.

For example, the horizontal driving circuit 6 is configured of the shiftregister and selects in turn each of the column signal processingcircuits 5 by sequentially outputting horizontal scanning pulses, andoutputs the pixel signal from each of the column signal processingcircuits 5 to a horizontal signal line 11.

The output circuit 7 outputs the signal by performing the signal processwith respect to the signals sequentially supplied from each of thecolumn signal processing circuits 5 through the horizontal signal line11. For example, the output circuit 7 may perform only buffering or mayperform black level adjustment, column variation correction, varioustypes of digital signal processes and the like. An input and outputterminal 13 exchanges a signal to and from the outside.

The solid-state imaging device 1 configured as described above is a CMOSimage sensor called a column AD type in which the column signalprocessing circuit 5 performing a CDS process and an AD conversionprocess is disposed for each pixel column.

2. Circuit Configuration Example of Pixel 2

FIG. 2 illustrates an equivalent circuit of the pixel 2.

The pixel 2 has a photodiode 21 as a photoelectric conversion element, afirst transfer transistor 22, a memory section (MEM) 23, a secondtransfer transistor 24, a floating diffusion (FD) 25, a reset transistor26, an amplification transistor 27, a selection transistor 28, and adischarge transistor 29.

The photodiode 21 is a photoelectric conversion section that generatesand accumulates charges (signal charges) depending on an amount ofreceived light. An anode terminal of the photodiode 21 is grounded and acathode terminal is connected to the memory section 23 through the firsttransfer transistor 22. Further, the cathode terminal of the photodiode21 is also connected to the discharge transistor 29.

When the first transfer transistor 22 is turned ON by a transfer signalTRX, the first transfer transistor 22 reads the charges generated in thephotodiode 21 and transfers the charges to the memory section 23. Thememory section 23 is a charge holding section that temporarily holds thecharges until the charges are transferred to the FD 25. When the secondtransfer transistor 24 is turned ON by a transfer signal TRG, the secondtransfer transistor 24 transfers the charges held in the memory section23 to the FD 25.

The FD 25 is a charge holding section that holds the charges that areread from the memory section 23 for reading the charges as a signal.When the reset transistor 26 is turned ON by a reset signal RST, apotential of the FD 25 is reset by discharging the charges held in theFD 25 to a constant voltage source VDD.

The amplification transistor 27 outputs the pixel signal depending onthe potential of the FD 25. That is, the amplification transistor 27configures a source follower circuit with a load MOS 14 as the constantvoltage source, and the pixel signal indicating a level depending on thecharges held in the FD 25 is output from the amplification transistor 27to the column signal processing circuit 5 (FIG. 1) through the selectiontransistor 28. For example, the load MOS 14 is provided inside thecolumn signal processing circuit 5.

The selection transistor 28 is turned ON when the pixel 2 is selected bya select signal SEL and outputs the pixel signal of the pixel 2 to thecolumn signal processing circuit 5 through the vertical signal line 9.The discharge transistor 29 discharges unnecessary charges that areaccumulated in the photodiode 21 to the constant voltage source VDD whenturned ON by a discharge signal OFG. The transfer signals TRX and TRG,the reset signal RST, the select signal SEL, and a discharge signal OFGare controlled by the vertical driving circuit 4 and are suppliedthrough the horizontal signal line 11 (FIG. 1).

An operation of the pixel 2 is simply described.

First, the discharge transistor 29 is turned ON by supplying thedischarge signal OFG of High level to the discharge transistor 29 beforethe exposure is started, and the charges accumulated in the photodiode21 are discharged to the constant voltage source VDD, and the photodiode21 is reset.

When the discharge transistor 29 is turned OFF by the discharge signalOFG of Low level after the photodiode 21 is reset, the exposure isstarted in all pixels.

When a predetermined exposure time that is determined in advance haselapsed, the first transfer transistor 22 is turned ON by a firsttransfer signal TRX in all pixels of the pixel array section 3, and thecharges accumulated in the photodiode 21 are transferred to the memorysection 23.

The charges held in the memory section 23 of each pixel 2 aresequentially read to an ADC 15 on a row-by-row basis after the firsttransfer transistor 22 is turned OFF. In the reading operation, thesecond transfer transistor 24 of the pixel 2 of a reading row is turnedON by a second transfer signal TRG and the charges held in the memorysection 23 are transferred to the FD 25. Then, the signal indicating thelevel depending on the charges held in the FD 25 are output from theamplification transistor 27 to the ADC 15 through the selectiontransistor 28 by the selection transistor 28 being turned ON by theselect signal SEL.

3. First Embodiment of Pixel 2

Schematic Configuration View of Pixel 2

Structures of the photodiode 21, the first transfer transistor 22, thememory section 23, the second transfer transistor 24 and the FD 25inside the pixel 2 are described with reference to FIGS. 3 to 4B.

FIG. 3 is a plan view illustrating a positional relationship between thephotodiode 21, the first transfer transistor 22, the memory section 23,the second transfer transistor 24 and the FD 25 inside the pixel 2.

FIG. 4A illustrates a cross-sectional view taken along line IVA-IVA ofFIG. 3 and FIG. 4B illustrates a cross-sectional view taken along lineIVB-IVB of FIG. 3.

Moreover, FIG. 3 is a plan view that is viewed from a surface side ofthe semiconductor substrate 12 that is an incident side of the light. InFIGS. 4A and 4B, an upper side of each view is the surface of thesemiconductor substrate 12 on which the light is incident.

As illustrated in FIG. 3, in each pixel 2 of the pixel array section 3,the photodiode 21, the first transfer transistor 22, the second transfertransistor 24 and the FD 25 are arranged in a predetermined direction.In FIG. 3, a lateral direction in which the photodiode 21, the firsttransfer transistor 22, the second transfer transistor 24 and the FD 25are arranged is referred to as a first direction.

In the left side inside the pixel 2 of the semiconductor substrate 12,the photodiode 21 is formed by forming an N-type semiconductor region 42that is a second conductivity type inside a P-type semiconductor region41 that is a first conductivity type.

Then, as illustrated in FIGS. 3 and 4A, a gate electrode 43 of the firsttransfer transistor 22 is formed on the right side of the photodiode 21,and an N-type semiconductor region 44 that is a charge holding region ofthe memory section 23 is formed on a lower side of the gate electrode43. The N-type semiconductor region 42 that is a charge accumulationregion of the photodiode 21 also serves as one side of a source/drainregion of the first transfer transistor 22, and the N-type semiconductorregion 44 that is a charge holding region of the memory section 23 alsoserves as the other side of the source/drain region of the firsttransfer transistor 22.

Further, as illustrated in FIG. 4B, the gate electrode 43 of the firsttransfer transistor 22 has a trench gate structure in which two trenchgate sections 43A are embedded in a depth direction of the semiconductorsubstrate 12. As illustrated in FIG. 3, the two trench gate sections 43Aare disposed so as to sandwich the N-type semiconductor region 44 thatis the memory section 23 from the second direction perpendicular to thefirst direction that is the transfer direction of the charges. Asillustrated in FIG. 4B, the depth of the trench gate section 43A that isembedded is substantially the same as that of the N-type semiconductorregion 44 of the memory section 23.

In other words, the N-type semiconductor region 44 that is the chargeholding region of the memory section 23 is formed vertically long alonga side wall of the two trench gate sections 43A of the first transfertransistor 22. Then, P-type/N-type/P-type semiconductor regions areformed in the horizontal direction between the two trench gate sections43A.

Moreover, in FIG. 3, the two trench gate sections 43A of the gateelectrode 43 of the first transfer transistor 22 and the N-typesemiconductor region 44 (the memory section 23) that is formed on thelower side of the gate electrode 43 are illustrated in broken lines.

Then, as illustrated in FIGS. 3 and 4A, a gate electrode 45 of thesecond transfer transistor 24 is formed on the opposite side to the sideon which the photodiode 21 is formed with respect to the gate electrode43 of the first transfer transistor 22, and an N-type semiconductorregion 46 that is the FD 25 is formed on the surface side of thesubstrate further on the right side thereof. The N-type semiconductorregion 44 that is the charge holding region of the memory section 23also serves as one side of the source/drain region of the secondtransfer transistor 24 and the N-type semiconductor region 46 that isthe FD 25 also serves as the other side of the source/drain region ofthe second transfer transistor 24.

Moreover, in FIGS. 4A and 4B, a multilayered wiring layer formed of aplurality of wiring layers and an interlayer insulating film, a colorfilter, an on-chip lens or the like is formed on an upper surface of thegate electrode 43 of the first transfer transistor 22 or the gateelectrode 45 of the second transfer transistor 24, which is the side ofthe light incident surface.

As described above, in the first embodiment of the pixel 2, the gateelectrode 43 of the first transfer transistor 22 has the transfer gatestructure in which the two trench gate sections 43A are embedded in thedepth direction of the semiconductor substrate 12. On the other hand,the gate electrode 45 of the second transfer transistor 24 has theplanar type gate structure that is formed only on the surface of thesemiconductor substrate.

Then, the N-type semiconductor region 44 as the memory section 23 isformed vertically long between the two trench gate sections 43A of thefirst transfer transistor 22 and the memory section 23 has a PN junctionsurface in the vertical direction that is the depth direction of thesubstrate.

Therefore, it is possible to provide the N-type semiconductor region 44as the memory section 23 without reducing the charge accumulation regionof the photodiode 21 and it is possible to prevent the light receptionsensitivity or the amount of the saturated charges from being loweredaccording to reduction of the area of the photodiode.

Manufacturing Method

A forming method of the gate electrode 43 of the first transfertransistor 22 and the N-type semiconductor region 44 that is the memorysection 23 is described with reference to FIGS. 5A to 5D.

First, as illustrated in FIG. 5A, a resist mask 61 is patterned so as toopen regions which form the two trench gate sections 43A and then theP-type semiconductor region 41 is etched to a predetermined depth.Therefore, two trench sections 62 which become the trench gate sections43A of the first transfer transistor 22 are formed.

Then, as illustrated in FIG. 5B, for example, P-type ions such as boron(B) are injected at low acceleration energy to the immediate vicinity ofthe side wall of the trench section 62.

Next, as illustrated in FIG. 5C, for example, N-type ions such asphosphorus (P) or arsenic (As) are injected. At this time, the ions areinjected at higher acceleration energy than that when P-type ions areinjected so as to inject the N-type ions into the inside from the sidewall of the trench section 62.

Moreover, the P-type ions and the N-type ions are injected with apredetermined tilt (tilt angle) so as to be incident obliquely to theside wall of the trench section 62.

Then, as illustrated in FIG. 5D, the resist mask 61 is peeled off andthen the gate electrode 43 of the first transfer transistor 22 isembedded in the trench sections 62 and is also formed on the surface ofthe semiconductor substrate 12. As a material of the gate electrode 43,for example, it is possible to employ polysilicon.

Through the above process, the gate electrode 43 of the first transfertransistor 22 including the two trench gate sections 43A is completedand the N-type semiconductor region 44 that is the charge holding regionof the memory section 23 is formed between the two trench gate sections43A.

Moreover, in the example of FIGS. 5A to 5D, the injection of the P-typeions is performed and then the injection of the N-type ions isperformed, but the order of the injection of the P-type ions and theinjection of the N-type ions may be reversed.

Pixel Structure of Planar Type First Transfer Transistor

In order to facilitate understanding of the effects of the pixelstructure to which the present technology is applied, the pixelstructure having the planar type first transfer transistor is describedwith reference to FIGS. 6 to 7B.

FIG. 6 is a plan view illustrating a positional relationship between aphotodiode 71, a first transfer transistor 72, a memory section 73, asecond transfer transistor 74, and a FD 75 of a pixel having a planartype first transfer transistor that is illustrated so as to correspondto FIG. 3.

Further, FIG. 7A illustrates a cross-sectional view taken along lineVIIA-VIIA of FIG. 6 and FIG. 7B illustrates a cross-sectional view takenalong line VIIB-VIIB of FIG. 6.

As illustrated in FIG. 6, the photodiode 71, the first transfertransistor 72, the second transfer transistor 74 and the FD 75 arearranged in a first direction similar to FIG. 3.

In the left side inside the pixel of a semiconductor substrate 60, thephotodiode 71 is formed by forming an N-type semiconductor region 62that is a second conductivity type inside a P-type semiconductor region61 that is a first conductivity type.

Then, as illustrated in FIGS. 6 and 7A, a gate electrode 63 of the firsttransfer transistor 72 is formed in a plane only on the surface of thesemiconductor substrate having an area greater than a light receivingarea of the photodiode 71 on the right side object photodiode 71, and anN-type semiconductor region 64 that is a charge holding region of thememory section 73 is formed to have a plane area at the same level asthe light receiving area of the photodiode 71 in the vicinity of thelower side of the gate electrode 63.

The N-type semiconductor region 62 that is a charge accumulation regionof the photodiode 71 also serves as one side of a source/drain region ofthe first transfer transistor 72 and the N-type semiconductor region 64that is a charge holding region of the memory section 73 also serves asthe other side of the source/drain region of the first transfertransistor 72.

Then, as illustrated in FIGS. 6 and 7A, the gate electrode 65 of thesecond transfer transistor 74 is formed on the opposite side to the sideon which the photodiode 71 is formed with respect to the gate electrode63 of the first transfer transistor 72, and an N-type semiconductorregion 66 that is the FD 75 is formed on the surface side of thesubstrate further on the right side thereof. The N-type semiconductorregion 64 that is the charge holding region of the memory section 73also serves as one side of the source/drain region of the secondtransfer transistor 74 and the N-type semiconductor region 66 that isthe FD 75 also serves as the other side of the source/drain region ofthe second transfer transistor 74.

As described above, in the pixel structure having the planar type firsttransfer transistor 72, since the N-type semiconductor region 64 that isthe charge holding region of the memory section 73 is formed in a planehaving a plane area at the same level as the light receiving area of thephotodiode 71, the charge accumulation region of the photodiode 71 issmall compared to the charge accumulation region of the photodiode 21described above. Thus, there is a problem that the light receptionsensitivity or the amount of the saturated charges of the photodiode islowered.

It is possible to increase a potential amplitude when the charges aredepleted and saturated and it is possible to increase the amount of thesaturated charges of the memory section 73 by increasing the impurityconcentration of the N-type semiconductor region 64 instead ofincreasing the area of the N-type semiconductor region 64 that is thecharge holding region of the memory section 73, but in this case,disadvantage occurs that the charge transfer is difficult.

Otherwise, it is possible to increase a junction capacity per unit areaand to increase the amount of the saturated charges of the memorysection 73 without changing the potential when the charges are depletedand accumulated by designing largely a junction electric field of theP-type and the N-type semiconductor regions of the memory section 73instead of increasing the area of the N-type semiconductor region 64that is the charge holding region of the memory section 73, but in thiscase, a disadvantage occurs that the noise is increased when dark by astrong junction electric field.

FIG. 8A illustrates an impurity concentration profile of a case wherethe N-type semiconductor region 64 of the memory section 73 is formed ina plane and the PN junction is formed on a horizontal surface asillustrated in FIGS. 7A and 7B.

The PN junction of the upper side of the N-type semiconductor region 64that is the charge holding region of the memory section 73 and the P-N-Pjunction that is the PN junction of the lower side of the N-typesemiconductor region 64 are formed in the depth direction of thesubstrate by injecting the ions from the surface side of thesemiconductor substrate 12. In this case, in principle, since theimpurity concentration profile spreads as the acceleration energyincreases, a junction capacity per unit area of the PN junction on thelower side of the memory section 73 is smaller than that of the PNjunction on the upper side of the memory section 73.

FIG. 8B is an impurity concentration profile in a case where, asillustrated in FIGS. 4A and 4B, the N-type semiconductor region 44 ofthe memory section 23 is vertically formed and the PN junction is formedon the vertical surface, and illustrates the impurity concentrationprofile between two trench gate sections 43A in line VIIIB-VIIIB of FIG.5D.

In the P-N-P junction between the two trench gate sections 43A, both thePN junction near the side wall of the trench section 62 of the rightside and the PN junction near the side wall of the trench section 62 ofthe left side are configured of an impurity profile that is formed bylow acceleration energy. Thus, both the PN junction of the right sideand the PN junction of the left side can realize high junction capacity.

Therefore, according to the pixel structure of the pixel 2 having the PNjunction surface in the vertical direction to which the presenttechnology is applied, it is also possible to increase the amount of thesaturated charges of the memory section 23 without lowering the amountof the saturated charges of the photodiode 21.

Modification Example of Manufacturing Method

A modification example of a forming method of an N-type semiconductorregion 44 that is a memory section 23 is described with reference toFIGS. 9A to 9C.

When the injection of the N-type ions is performed, it is possible tochange the impurity concentration of the N-type semiconductor region 44that is the memory section 23 depending on the depth thereof by changingthe tilt angle of the injection of the ions depending on the depth ofthe substrate of the trench section 62.

For example, the injection of the N-type ions is performed so that arelationship of θ₁<θ₂<θ₃ is satisfied when the tilt angle of theinjection of the ions in a deep position of the trench section 62illustrated in FIG. 9A is θ₁, the tilt angle of the injection of theions in an intermediate position of the trench section 62 illustrated inFIG. 9B is θ₂ and the tilt angle of the injection of the ions in ashallow position of the trench section 62 illustrated in FIG. 9C is θ₃.

Therefore, the impurity concentration of the N-type semiconductor region44 of the memory section 23 becomes thick in the shallow position of thesurface side of the substrate and becomes thin in the deep position. Inother words, the potential of the N-type semiconductor region 44 of thememory section 23 is high in the shallow position of the surface side ofthe substrate and is low in the deep position thereof.

By doing so, when reading the charges from the memory section 23, it ispossible to generate the electric field to assist the charge transferand to facilitate the reading of the charges from the memory section 23.

Moreover, the impurity concentration of the N-type semiconductor region44 of the memory section 23 may not change in proportion to the depthbut the semiconductor region 44 may be divided into a plurality ofregions in the depth direction and the impurity concentration may becomethick as moving to the surface side of the substrate.

4. Second Embodiment of Pixel 2

A second embodiment of the pixel 2 is described with reference to FIGS.10 and 11.

FIG. 10 is a plan view illustrating a positional relationship between aphotodiode 21, a first transfer transistor 22, a memory section 23, asecond transfer transistor 24 and a FD 25 inside the pixel 2 in thesecond embodiment.

FIG. 11 illustrates a cross-sectional view taken along line XI-XI ofFIG. 10.

In FIGS. 10 and 11, the same reference numerals are given to the sameportions corresponding to FIGS. 3 to 4B in the first embodiment anddescription of portions duplicating those of the first embodiment isomitted.

As illustrated in FIG. 11, the two trench gate sections 43A of the gateelectrode 43 of the first transfer transistor 22 are formed in the firstembodiment, but three trench gate sections 43A thereof are formed in thesecond embodiment. Therefore, two regions are formed between the twotrench gate sections 43A and the N-type semiconductor region 44 that isthe charge holding region of the memory section 23 is formed in eachregion. That is, two N-type semiconductor regions 44 are formed as thecharge holding region of the memory section 23.

Further, as illustrated in FIG. 10, the area of the N-type semiconductorregion 46 in the plane direction that is the FD 25 is also formedlargely corresponding to two N-type semiconductor regions 44.

It is possible to further increase the amount of the saturated chargesof the memory section 23 by having the configuration as described above.

Moreover, the number of the trench gate sections 43A of the gateelectrode 43 of the first transfer transistor 22 may be four or more.

5. Third Embodiment of Pixel 2

A third embodiment of the pixel 2 is described with reference to FIGS.12 and 13.

FIG. 12 is a plan view illustrating a positional relationship between aphotodiode 21, a first transfer transistor 22, a memory section 23, asecond transfer transistor 24 and a FD 25 inside the pixel 2 in thethird embodiment.

FIG. 13 illustrates a cross-sectional view taken along line XIII-XIII ofFIG. 12.

In FIGS. 12 and 13, the same reference numerals are given to the sameportions corresponding to FIGS. 3 to 4B in the first embodiment anddescription of portions duplicating those of the first embodiment isomitted.

In the pixel structure to which the present technology is applied, sincethe N-type semiconductor region 44 of the memory section 23 is formed toa deep position of the semiconductor substrate 12, the light incident tothe photodiode 21 may come around the memory section 23 and noise may begenerated by the light that is incident coming around.

Thus, in the third embodiment, a structure that prevents the light fromcoming around the N-type semiconductor region 44 of the memory section23 is added to the structure that is illustrated as the firstembodiment.

Specifically, as illustrated in FIG. 13, a light-shielding section 101Ais formed by embedding a light-shielding material such as tungsten (W)inside two trench gate sections 43A of the gate electrode 43 of thefirst transfer transistor 22.

Further, as illustrated in FIGS. 12 and 13, a light-shielding section101B is formed by a light-shielding material similar to thelight-shielding section 101A so as to cover an upper surface and sidesurfaces of the gate electrode 43 of the first transfer transistor 22.

Moreover, in the plan view of FIG. 12, illustration of thelight-shielding section 101B formed on the upper surface of the gateelectrode 43 of the first transfer transistor 22 is omitted.

It is possible to prevent the light from coming around the N-typesemiconductor region 44 of the memory section 23 and to suppressoccurrence of the noise by having the configuration as described above.

Further, it is possible to increase the amount of the saturated chargesof the memory section 23 without lowering the amount of the saturatedcharges of the photodiode 21 by forming vertically long the N-typesemiconductor region 44 as the memory section 23 between the two trenchgate sections 43A of the first transfer transistor 22.

6. Fourth Embodiment of Pixel 2

A fourth embodiment of the pixel 2 is described with reference to FIGS.14 to 15B.

The pixel structure of the first to third embodiments described above isdescribed as the surface irradiation type pixel structure, but it ispossible to be applied to any of the surface irradiation type and a backsurface irradiation type.

Meanwhile, hereinafter, a pixel structure that is the pixel structure towhich the present technology is applied and is specified as having theback surface irradiation type is described.

FIG. 14 is a plan view illustrating a positional relationship between aphotodiode 21, a first transfer transistor 22, a memory section 23, asecond transfer transistor 24 and a FD 25 inside the pixel 2 in thefourth embodiment. However, FIG. 14 is different from the plan views inthe first to third embodiments described above in that the plan view isviewed from a surface of the opposite side to the surface on which thelight of the semiconductor substrate 12 is incident.

FIG. 15A illustrates a cross-sectional view taken along line XVA-XVA ofFIG. 14 and FIG. 15B illustrates a cross-sectional view taken along lineXVB-XVB of FIG. 14.

In FIGS. 14 to 15B, the same reference numerals are given to the sameportions corresponding to FIGS. 3 to 4B in the first embodiment anddescription of portions duplicating those of the first embodiment isomitted.

In FIGS. 15A and 15B, the upper side of the view is the back surfaceside of the semiconductor substrate 12 on which the light is incidentand a color film, an on-chip lens or the like is laminated on the upperside of the view of the semiconductor substrate 12.

Meanwhile, as illustrated in FIGS. 15A and 15B, the gate electrode 43 ofthe first transfer transistor 22, the gate electrode 45 of the secondtransfer transistor 24 or the like is formed on the lower side of theview of the semiconductor substrate 12. Further, although notillustrated, a multilayered wiring layer that is formed of a pluralityof wiring layers and an interlayer insulation film is formed on thelower side of the gate electrode 43 of the first transfer transistor 22and the gate electrode 45 of the second transfer transistor 24.

The fourth embodiment is similar to the first embodiment described abovein that two trench gate sections 43A of the gate electrode 43 of thefirst transfer transistor 22 are embedded in the depth direction of thesemiconductor substrate 12, and the N-type semiconductor region 44 ofthe memory section 23 is formed vertically long between the two trenchgate sections 43A.

However, since the pixel of the fourth embodiment is the back surfaceirradiation type pixel, the two trench gate sections 43A of the gateelectrode 43 of the first transfer transistor 22 extend upward from theback surface side of the semiconductor substrate 12 of the lower side ofthe view.

Further, also in the fourth embodiment, the structure to prevent thelight from coming around the N-type semiconductor region 44 of thememory section 23 is employed. That is, as illustrated in FIGS. 15A and15B, in order to prevent the light from coming around the memory section23, a light-shielding section 111 is formed on the back surface that isthe side of the light incident surface, and side surfaces to surroundthe two trench gate sections 43A of the first transfer transistor 22 andthe memory section 23.

In the back surface irradiation type pixel structure, it is possible toprevent the light from coming around the N-type semiconductor region 44that is the memory section 23 and to suppress occurrence of the noise byhaving the configuration described above.

Further, it is also possible to increase the amount of the saturatedcharges of the memory section 23 without lowering the amount of thesaturated charges of the photodiode 21 by forming vertically long theN-type semiconductor region 44 as the memory section 23 between the twotrench gate sections 43A of the first transfer transistor 22.

7. Fifth Embodiment of Pixel 2

A fifth embodiment of the pixel 2 is described with reference to FIGS.16 to 17B.

The pixel structure of the fifth embodiment is also an example of theback surface irradiation type similar to the fourth embodiment.

FIG. 16 is a plan view illustrating a positional relationship between aphotodiode 21, a first transfer transistor 22, a memory section 23, asecond transfer transistor 24 and a FD 25 inside the pixel 2 viewed fromthe surface of the opposite side to the light incident side of thesemiconductor substrate 12 in the fifth embodiment.

FIG. 17A illustrates a cross-sectional view taken along line XVIIA-XVIIAof FIG. 16 and FIG. 17B illustrates a cross-sectional view taken alongline XVIIB-XVIIB of FIG. 16.

In FIGS. 16 to 17B, the same reference numerals are given to the sameportions corresponding to FIGS. 3 to 4B in the first embodiment anddescription of portions duplicating those of the first embodiment isomitted.

In the fifth embodiment, as illustrated in FIGS. 17A and 17B, alight-shielding photoelectric conversion film 121 is formed on an entiresurface of the back surface side of the semiconductor substrate 12 thatis a surface on which the light is incident. Moreover, a color filter oran on-chip lens (not illustrated) is formed on further upper surface ofthe photoelectric conversion film 121.

For example, the photoelectric conversion film 121 can be formed of acompound semiconductor having a chalcopyrite structure formed ofcopper-aluminum-gallium-indium-sulfur-selenium-based mixed crystal.

In the pixel structure of the fifth embodiment, since the photoelectricconversion film 121 functions as the light-shielding film, it ispossible to prevent the light from coming around the N-typesemiconductor region 44 as the memory section 23 and to suppressoccurrence of the noise by a further simpler configuration withoutnecessity to provide the light-shielding section 111 as in the fourthembodiment.

Further, it is also possible to increase the amount of the saturatedcharges of the memory section 23 without lowering the amount of thesaturated charges of the photodiode 21 by forming vertically long theN-type semiconductor region 44 as the memory section 23 between the twotrench gate sections 43A of the first transfer transistor 22.

8. Application Example to Electronic Apparatus

The present technology is not limited to the application to thesolid-state imaging device. That is, the present technology may beapplied to an electronic apparatus in general using a solid-stateimaging device in an image capturing section (photoelectric convertor)such as an imaging device such as a digital still camera or a digitalvideo camera, a mobile terminal device having an imaging function, and acopy machine using a solid-state imaging device in the image readingunit. The solid-state imaging device may have a form that is formed asone chip or may be a form of a module having the imaging function whichis packaged with the imaging section, the signal processor or an opticalsystem.

FIG. 18 is a block diagram illustrating a configuration example of animaging apparatus as an electronic apparatus to which the presenttechnology is applied.

An imaging apparatus 200 illustrated in FIG. 18 includes an opticalsection 201 formed of a lens group and the like, a solid-state imagingdevice (imaging device) 202 in which the configuration of thesolid-state imaging device 1 of FIG. 1 is employed, and a Digital SignalProcessor (DSP) circuit 203 that is a camera signal process circuit.Further, the imaging apparatus 200 includes a frame memory 204, adisplay section 205, a recording section 206, an operation section 207,and a power supply section 208. The DSP circuit 203, the frame memory204, the display section 205, the recording section 206, the operationsection 207, and the power supply section 208 are connected to eachother through a bus line 209.

The optical section 201 forms an image on an imaging surface of thesolid-state imaging device 202 by capturing incident light (image light)from an object. The solid-state imaging device 202 converts an amount ofthe incident light in which the image is formed on the imaging surfaceby the optical section 201 into an electric signal in pixel units andthen outputs the electric signal as the pixel signal. As the solid-stateimaging device 202, it is possible to use a solid-state imaging devicesuch as the solid-state imaging device 1 of FIG. 1, that is, thesolid-state imaging device that has the pixel structure in which thefirst transfer transistor 22 has the trench gate structure and thememory section 23 having the vertical PN junction is included between aplurality of trench gate sections 43A which are embedded in the depthdirection of the substrate.

For example, the display section 205 is formed of a panel type displaydevice such as a liquid crystal panel or an electro-luminescence (EL)panel, and displays a moving image or a still image that is imaged inthe solid-state imaging device 202. The recording section 206 recordsthe moving image or the still image that is captured in the solid-stateimaging device 202 on a recording medium such as a hard disk or asemiconductor memory.

The operation section 207 issues operation commands with respect tovarious functions held in the imaging apparatus 200 under the operationof a user. The power supply section 208 appropriately supplies variouspowers which are operation powers of the DSP circuit 203, the framememory 204, the display section 205, the recording section 206, and theoperation section 207 to the objects to be supplied.

As described above, as the solid-state imaging device 202, it ispossible to increase the area of the photodiode and to realize highsensitivity by using the solid-state imaging device 1 according to theembodiments described above. Therefore, also in the imaging apparatus200 such as the video camera, the digital still camera, or a cameramodule for a mobile device such as a mobile phone, it is possible toachieve high image quality in a captured image.

In the embodiment described above, the solid-state imaging device isdescribed in which the first conductivity type is the P-type, the secondconductivity type is the N-type and electrons are the signal charges,but the present technology can be also applied to a solid-state imagingdevice in which positive holes are the signal charges. That is, it ispossible to configure each semiconductor region described above as areversed conductivity type semiconductor region in which the firstconductivity type is the N-type and the second conductivity type is theP-type.

Further, the present technology is not limited to the application to thesolid-state imaging device that captures the image by detecting thedistribution of the incident quantity of light of visible light and maybe applied to a solid-state imaging device that captures distribution ofan incident quantity of infrared rays, X-rays, particles and the like asan image, or, in a broader sense, a solid-state imaging device (aphysical quantity distribution detection device) in general such as afingerprint detection sensor that captures an image by detectingdistribution of other physical quantities such as a pressure or anelectrostatic capacitance.

An applicable embodiment of the present technology is not limited to theembodiment described above and may be variously modified withoutdeparting from the scope of the present technology.

For example, it is possible to employ a form that combines all or aportion of a plurality of embodiments described above.

Moreover, the effects described in the specification are onlyillustrative and are not intended to be limited, and there may beeffects other than those described in the specification.

Further, the present technology may be configured as described below.

(1) A solid-state imaging device including: a pixel having aphotoelectric conversion section that generates and accumulates chargesdepending on an amount of received light, a charge accumulation sectionthat accumulates the charges that are generated by the photoelectricconversion section, a first transfer transistor that transfers thecharges of the photoelectric conversion section to the chargeaccumulation section, a charge holding section that holds the chargesfor reading the charges as a signal, and a second transfer transistorthat transfers the charges of the charge accumulation section to thecharge holding section, in which a gate electrode of the first transfertransistor has two or more trench gate sections embedded from aninterface of a semiconductor substrate to a predetermined depth, and inwhich the charge accumulation section is formed vertically long betweentwo trench gate sections of the first transfer transistor embedded inthe semiconductor substrate.

(2) The solid-state imaging device according to (1), in which the chargeaccumulation section has a PN junction surface in a vertical directionthat is a depth direction of the semiconductor substrate.

(3) The solid-state imaging device according to (1) or (2), in which afirst conductivity type/a second conductivity type/the firstconductivity type semiconductor regions are formed between the twotrench gate sections of the first transfer transistor.

(4) The solid-state imaging device according to any one of (1) to (3),in which the charge accumulation section has a semiconductor regionhaving different impurity concentrations in the depth direction of thesemiconductor substrate.

(5) The solid-state imaging device according to any one of (1) to (4),in which the gate electrode of the first transfer transistor has twotrench gate sections embedded from the interface of the semiconductorsubstrate to a predetermined depth.

(6) The solid-state imaging device according to any one of (1) to (5),in which the gate electrode of the first transfer transistor has threetrench gate sections embedded from the interface of the semiconductorsubstrate to a predetermined depth.

(7) The solid-state imaging device according to any one of (1) to (6),in which a light-shielding material is embedded inside the trench gatesection of the first transfer transistor.

(8) The solid-state imaging device according to any one of (1) to (7),in which the solid-state imaging device has back surface irradiationtype device in which light is incident from a back surface of thesemiconductor substrate.

(9) The solid-state imaging device according to (8), in which alight-shielding section is formed in a back surface and side surfacessurrounding the two or more trench gate sections and the chargeaccumulation section therebetween.

(10) The solid-state imaging device according to (8), in which alight-shielding photoelectric conversion film is formed on the backsurface that is a side of a light incident surface of the semiconductorsubstrate.

(11) A manufacturing method of a solid-state imaging device, in a casewhere a pixel which has a photoelectric conversion section thatgenerates and accumulates charges depending on an amount of receivedlight, a charge accumulation section that accumulates the charges thatare generated by the photoelectric conversion section, a first transfertransistor that transfers the charges of the photoelectric conversionsection to the charge accumulation section, a charge holding sectionthat holds the charges for reading the charges as a signal, and a secondtransfer transistor that transfers the charges of the chargeaccumulation section to the charge holding section, and in which a gateelectrode of the first transfer transistor has two or more trench gatesections embedded from an interface of a semiconductor substrate to apredetermined depth is formed, including: forming a trench section thatis formed of trench gate sections; and forming a PN junction surface ina vertical direction that is a depth direction of the semiconductorsubstrate between the two trench sections by injecting a secondconductivity type ion at a predetermined tilt angle after injecting afirst conductivity type ion at a predetermined tilt angle with respectto the trench section.

(12) The manufacturing method of a solid-state imaging device accordingto (11), in which acceleration energy is different between the firstconductivity type ion injection and the second conductivity type ioninjection.

(13) The manufacturing method of a solid-state imaging device accordingto (11) or (12), in which in the first or second conductivity type ioninjection for forming a semiconductor region becoming the chargeaccumulation section, the predetermined tilt angle varies with depth ofthe semiconductor substrate.

(14) An electronic apparatus including a solid-state imaging deviceincluding a pixel having a photoelectric conversion section thatgenerates and accumulates charges depending on an amount of receivedlight, a charge accumulation section that accumulates the charges thatare generated by the photoelectric conversion section, a first transfertransistor that transfers the charges of the photoelectric conversionsection to the charge accumulation section, a charge holding sectionthat holds the charges for reading the charges as a signal, and a secondtransfer transistor that transfers the charges of the chargeaccumulation section to the charge holding section, in which a gateelectrode of the first transfer transistor has two or more trench gatesections embedded from an interface of a semiconductor substrate to apredetermined depth, and in which the charge accumulation section isformed vertically long between two trench gate sections of the firsttransfer transistor embedded in the semiconductor substrate.

(1′) A solid-state imaging device, comprising: a pixel including aphotoelectric conversion element configured to generate a charge inresponse to incident light, a first transfer gate configured to transferthe charge from the photoelectric conversion element to a charge holdingsection, and a second transfer gate configured to transfer the chargefrom the charge holding section to a floating diffusion, wherein thefirst transfer gate includes a trench gate structure having at least twotrench gate sections embedded in a depth direction of a semiconductorsubstrate, and the charge holding section includes a semiconductorregion positioned between adjacent ones of the plurality of trench gatesections.

(2′) The solid-state imaging device according to (1′), whereinrespective ones of the at least two trench gate sections have adimension in the depth direction which is larger than a dimension in adirection perpendicular to the depth direction.

(3′) The solid-state imaging device according to (1′) or (2′), wherein adepth of respective ones of the at least two trench gate sections issubstantially the same as a depth of the semiconductor region.

(4′) The solid-state imaging device according to any one of (1′) to(3′), wherein the semiconductor substrate has a first conductivity typeand the semiconductor region has a second conductivity type which isopposite the first conductivity type.

(5′) The solid-state imaging device according to (4′), wherein a portionof the semiconductor substrate is disposed between the semiconductorregion and respective ones of the at least two trench gate sections.

(6′) The solid-state imaging device according to (5′), wherein the firstconductivity type is P-type, and the second conductivity type is N-type.

(7′) The solid-state imaging device according to (5′), wherein the firstconductivity type is N-type, and the second conductivity type is P-type.

(8′) The solid-state imaging device according to any one of (1′) to(7′), wherein the semiconductor region also serves as one of a source ora drain of the second transfer gate.

(9′) The solid-state imaging device according to any one of (1′) to(8′), wherein the first transfer gate further includes a light-shieldingsection.

(10′) The solid-state imaging device according to (9′), wherein thelight-shielding section includes a portion embedded in respective onesof the at least two trench gate sections.

(11′) The solid-state imaging device according to (9′), wherein thelight-shielding section includes a portion covering an upper surface andside surfaces of the first transfer gate.

(12′) The solid-state imaging device according to (9′), wherein amaterial of the light-shielding section is tungsten.

(13′) The solid-state imaging device according to any one of (1′) to(12′), wherein the at least two trench gate sections is at least threetrench gate sections.

(14′) The solid-state imaging device according to any one of (1′) to(13′), wherein a material of the first transfer gate is polysilicon.

(15′) The solid-state imaging device according to any one of (1′) to(14′), wherein the pixel further comprises a discharge gate configuredto discharge charges accumulated in the photoelectric conversionelement.

(16′) The solid-state imaging device according to any one of (1′) to(15′), wherein the pixel further comprises a reset gate configured todischarge charges held in the floating diffusion.

(17′) The solid-state imaging device according to any one of (1′) to(16′), wherein the pixel is a back-side illumination type.

(18′) A method of manufacturing a solid-state imaging device,comprising: providing a semiconductor substrate; forming a pixel on thesemiconductor substrate, the pixel including a photoelectric conversionelement configured to generate a charge in response to incident light, afirst transfer gate configured to transfer the charge from thephotoelectric conversion element to a charge holding section, and asecond transfer gate configured to transfer the charge from the chargeholding section to a floating diffusion, wherein the first transfer gateincludes a trench gate structure having at least two trench gatesections embedded in a depth direction of a semiconductor substrate, andthe charge holding section includes a semiconductor region positionedbetween adjacent ones of the plurality of trench gate sections.

(19′) An electronic apparatus, comprising: an optical section; asolid-state imaging device; and a digital signal processor circuit,wherein the solid-state imaging device includes: a pixel including aphotoelectric conversion element configured to generate a charge inresponse to incident light, a first transfer gate configured to transferthe charge from the photoelectric conversion element to a charge holdingsection, and a second transfer gate configured to transfer the chargefrom the charge holding section to a floating diffusion, wherein thefirst transfer gate includes a trench gate structure having at least twotrench gate sections embedded in a depth direction of a semiconductorsubstrate, and the charge holding section includes a semiconductorregion positioned between adjacent ones of the plurality of trench gatesections.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A pixel circuit, comprising: a gate electrodedisposed on a first surface of a semiconductor substrate; aphotoelectric conversion film disposed on a second surface of thesemiconductor substrate opposite the first surface; a source region; anda drain region, wherein the gate electrode has a trench gate structureincluding at least two trench gate sections embedded in a depthdirection of the semiconductor substrate and a connecting portionconnecting the at least two trench gate sections, and one of the sourceregion or the drain region is disposed between adjacent ones of the atleast two trench gate sections and underneath the connecting portion. 2.The pixel circuit according to claim 1, wherein respective ones of theat least two trench gate sections have a dimension in the depthdirection that is larger than a dimension in a direction perpendicularto the depth direction.
 3. The pixel circuit according to claim 1,wherein a depth of respective ones of the at least two trench gatesections is substantially the same as a depth of the one of the sourceregion or the drain region.
 4. The pixel circuit according to claim 1,wherein the semiconductor has a first conductivity type and the one ofthe source region or the drain region has a second conductivity typethat is opposite the first conductivity type.
 5. The pixel circuitaccording to claim 4, wherein the first conductivity type is P-type, andthe second conductivity type is N-type.
 6. The pixel circuit accordingto claim 4, wherein the first conductivity type is N-type, and thesecond conductivity type is P-type.
 7. The pixel circuit according toclaim 1, wherein the semiconductor substrate includes a first portiondisposed between a first trench gate section of the at least two trenchgate sections and the one of the source region or the drain region, anda second portion disposed between a second trench gate section of the atleast two trench gate sections and the one of the source region or thedrain region.
 8. The pixel circuit according to claim 1, wherein thephotoelectric conversion film is formed of a compound semiconductorhaving a chalcopyrite structure.
 9. The pixel circuit according to claim8, wherein the compound semiconductor is formed of acopper-aluminum-gallium-indium-sulfur-selenium-based mixed crystal. 10.The pixel circuit according to claim 1, wherein the second surface is alight-incident surface.
 11. The pixel circuit according to claim 1,further comprising a color filter on an upper surface of thephotoelectric conversion film.
 12. The pixel circuit according to claim1, further comprising an on-chip lens formed on an upper surface of thephotoelectric conversion film.
 13. The pixel circuit according to claim1, wherein a material of the gate electrode is polysilicon.
 14. Thepixel circuit according to claim 1, wherein the at least two trench gatesections is at least three trench gate sections.
 15. A method ofmanufacturing a pixel circuit, comprising: providing a semiconductorsubstrate, the semiconductor substrate having a first surface and asecond surface opposite the first surface; forming a transistor on thefirst surface of the semiconductor substrate, the transistor including agate electrode disposed on the semiconductor substrate, a source region,and a drain region; and forming a photoelectric conversion film on thesecond surface of the semiconductor substrate, wherein the gateelectrode has a trench gate structure including at least two trench gatesections embedded in a depth direction of the semiconductor substrateand a connecting portion connecting the at least two trench gatesections, and one of the source region or the drain region is disposedbetween adjacent ones of the at least two trench gate sections andunderneath the connecting portion.
 16. The method according to claim 15,wherein the photoelectric conversion film is formed of a compoundsemiconductor having a chalcopyrite structure.
 17. The method accordingto claim 16, wherein the compound semiconductor is formed of acopper-aluminum-gallium-indium-sulfur-selenium-based mixed crystal. 18.The method according to claim 15, wherein the second surface is alight-incident surface.
 19. The method according to claim 15, furthercomprising forming a color filter on an upper surface of thephotoelectric conversion film.
 20. The method according to claim 15,further comprising forming an on-chip lens on an upper surface of thephotoelectric conversion film.